Centralized traffic controlling system for railroads



Jan 26, 1937. w T, POWELL 2,068,931

M FOR RAILROADS CENTRALIZED TRAFFIC CONTROLLING SYSTE 5 Sheets-Sheet 1 Filed April 28, 1954 INVITO ATTORNEY h 28 1 .m 2 m n Jan. 26, 1937. I w. T. POWELL 1 2,068,931

CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Filed April 28, 1954 5Sheets-Sheet 2 A Line FIG. 2A.

Jan. 26, 1937.

w. T. POWELL CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Filed April 28, 1934 5 Sheets-Sheet 3 ATTORN EY Jan. 26, 1937. w. T. POWELL 2,068,931

CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS 5 Sheets-Sheet 4 Filed April 28, 1954 mad, BY Mum m w HF.

ATTORNEY Jan. 26, 1937. w. POWELL 2,068,931

CENTRALIZED TRAFFIC'CONTROLLING SYSTEM FOR RAILROADS Filed April 28, 1954 5 Sheets-Sheet 5 B'Y EBVM Patented Jan. 26, 1937 UNITED STATES PATENT OFFEQE GENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Application April 28, 1934, Serial No. 722,892

21 Claims.

This invention relates to centralized trafilc controlling systems for governing traific on railroads and it more particularly pertains to the communication part of such systems.

In a centralized traffic controlling system of the type contemplated by this invention the switches and signals at various locations along a railroad system are placed under the control of an operator in a central control office in such a way that the operator may change the positions of the switches subject to automatic operation and detector locking circuits, which prevent unsafe operation of any switch and in such a way that the operator may hold any of the signals at stop or allow them to clear, depending upon the position of the associated switches and provided the location of trains makes it safe for such signals to indicate proceed. Means are also provided in the system whereby indications are displayed in the control office to inform the operator of the presence or absence of trains on the various track sections throughout the territory under his supervision and to indicate the posi-- tions and conditions of the various switches, signals and the like.

The switches and signals are distributed throughout the territory but the apparatus provided to govern the switches and signals which are located relatively near each other is conveniently termed a field station. A communication system is provided to interconnect the control office with the several field stations for the transmission of controls to the field stations and for the reception of indications from the field stations.

In accordance with the present invention the communication system is provided with two line wires connecting the control office with all of the field stations and for convenience in describing the invention these line wires will be referred to as the A line and the B line. These two line wires serve the purpose of carrying the impulses which are used to select the required station and for transmitting controls to the selected station, as well as serving to register a calling station in the control ofiice and transmitting indications to the control ofllce from the registered station.

The system is of the coded duplex type, that is, it is operated through cycles of operation for the transmission of controls and/or the transmission of indications during each cycle. When controls are transmitted a station selecting code is first applied to the line circuit for selecting the particular station with which communication is desired and then the controls are transmitted to that station by means of additional code impulses. When indications are transmitted the particular field station transmitting such indications first transmits a station registering code for registering the transmitting station in the control office and then the indications from this registered station are transmitted to the control ofiice by means of additional code impulses.

For the transmission of controls a predetermined number of impulses of selected polarities are placed on the line circuit for operating the apparatus at the control office and at the field stations in synchronism through cycles of opertion, irrespective of the character of the impulses. The distinctive character of the impulses of each series determines the particular station to be selected and the controls to be transmitted to the selected station.

For the transmission of indications a predetermined number of impulses are placed on the line circuit for operating the apparatus at the control office and at the field stations in synchronism through a cycle of operation. During a cycle for the transmission of indications alone the apparatus at all field stations and the apparatus at the control office are operated, with the impulses placed on the control line circuit of a nonselecting character so that no station is selected for controls during this cycle.

The transmitting field station is arranged to unbalance a normally balanced Wheatstone bridge which is set up at the beginning of a cycle, with the line circuit located in one arm of this bridge. The transmitting field station conditions this balanced line circuit at each step of the cycle, so that it will either be unbalanced or left in its balanced condition for forming a station registering code which is effective to register the calling station in the control oflice. After the calling station is registered in the office, indications are transmitted from the registered station by unbalancing or leaving balanced the Wheatstone bridge.

One feature of the present invention resides in the manner in which the communication system is made up into a Wheatstone bridge at the beginning of a cycle and the manner in which this bridge is balanced and unbalanced to provide for the transmission of indications.

Another feature of the present invention re sides in the manner in which each impulse period of the line circuit is divided into two parts, with the above mentioned balancing and unbalancing efiected in both parts of each impulse period. This transmission of indications twice during each step increases the capacity to substantially double the capacity of the system for the transmission of controls. This is particularly desirable in a centralized traific controlling system, since it has been found in practice that the number of indications desired by the operator to supply proper information is substantially double the number of controls necessary.

Another feature of the present invention resides in the manner in which the apparatus functions for the transmission of controls over the communication system in the same cycle of operations during which the transmission of indications is efiected.

Another feature of the present invention resides in the manner in which the apparatus at all field stations is initiated into operation from the control office. This is accomplished by applying a momentary impulse of alternating current to the line circuit for energizing a start relay which is connected to the line at each station. Each starting relay is connected to the line circuit in series with a condenser so that the line is normally deenergized, although the control ofiice battery is normally connected to the line circuit for the purpose of conveniently starting a. cycle of operations when a field station completes a direct current circuit for this battery.

These characteristic features of the present invention thus briefly stated will be explained more in detail in the following description of one embodiment of the invention, while various other characteristic features, functions and advantages of a system embodying this invention will be in I part pointed out and in part apparent as the description progresses.

In describing the invention in detail reference. will be made to the accompanying drawings, in which those parts having similar features and functions are designated throughout the drawings by like letter reference characters which are generally made distinctive, either by reason of distinctive exponents representative of their location in the system or by reason of preceding nu merals representative of the order of their operation during a cycle and in which:

Fig. 1A illustrates in schematic manner the fundamental layout of the line circuit in the form of a Wheatstone bridge.

Fig. 1B illustrates the line circuit in its normal condition, showing the line relay and resistance coil in series with the line battery in the office and the starting relays in series with their associated condensers bridged across the line at each field station.

Fig. 10 illustrates the circuit condition of the line during impulsing.

Figs. 2A and 2B illustrate the apparatus and circuit arrangement-s employed at the control oflice for providing means whereby the operator may select the stations and govern the switches and signals throughout the territory and also for providing means whereby indications may be received from the various field stations throughout such territory.

Figs. 3A and 3B illustrate the apparatus and circuit arrangements employed at a typical field station for providing selection of this station and the control of a single track switch in accordance with the present invention, as well as providing for the transmission of indications to the control oifice.

For the purpose of simplifying the drawings and facilitating in the explanation various parts and circuits have been shown diagrammatically and certain conventional illustrations have been employed. The drawings have been made more with the purpose of making it easy to understand the operation of the system rather than with the idea of illustrating the specific arrangement that would preferably be employed in practice. For example, the various relays and their contacts are illustrated in a conventional manner and symbols are used to indicate the connections to the terminals of batteries or other sources of electric current instead of showing all of the wiring connections to these terminals.

The symbols and are employed to indicate the positive and negative terminals respectively of suitable batteries or other sources of current and the circuits with which these symbols are used always have current flowing in the same direction. The symbols (B+) and (B) are employed to indicate the positive and negative terminals respectively of suitable batteries or other sources of current having mid-taps designated (CN) and the symbols with which these circuits are used may have current flowing in one direction or the other, depending upon whether the terminal (3+) or (B-( is used in combination with the center-tap (CN).

Communication sy-Stem.-The general plan of organization of this system may be best understood by reierring to Figs. 1A, 1B and 10 which illustrate schematically the line circuit and the portion of the apparatus more directly associated with the line circuit in a system having a control office and three field stations. It is to be understood that the system may be operated with as many field stations as desired but for convenience in describing the present invention three stations have been indicated as connected to the line circuit in Figs. 1B and 10. It will also be understood that the field stations, irrespective of their num her, are connected in series in the line circuit during impulsing in arm b of the Wheatstone bridge illustrated in Fig. 1A.

The detailed circuit arrangement and operation of the system in detail may be more readily understood by considering the drawings with Fig. 2A placed above Fig. 23, with Fig. 3A placed above Fig. 3B, and with Fig. 3A placed to the right of Fig. 2A, with correspondingly numbered lines in alinement.

Control oflice equipment-The control ofiice includes a control machine having a group of control levers for each of the field stations, a miniature track layout corresponding to the actual track layout in the field and various indicating lamps or the like, together with apparatus and circuits to accomplish the desired functions of the system.

That part of the control oflicc illustrated shows more particularly that part of a control machine which is typical of the apparatus associated with a single field station having a track switch, together with the general transmitting apparatus employed for all such field stations in the system.

The apparatus for one track switch comprises a switch machine control lever SML, a starting button SB, a miniature track switch is, a track occupancy indicating lamp OS and switch machine position indicating lamps N and R. Lilacwise a signal control lever or levers (not shown) would also be associated with the miniature track switch, but for convenience this apparatus has been omitted since the control of a tracl: switch may be considered as typical of the control of other types of trafiic controlling devices.

The actuations of lever SML from one extreme position to the other, followed by the actuation of button SB result in the normal or reverse positioning of the corresponding track switch at the corresponding field station as controlled through the medium of the communica tion system. The momentary actuation of button SB is stored by storing relay SR which in turn picks up the corresponding code determining relay CD for the associated station. There is one storing relay and one code determining relay for each station in the system and they are so interlocked that irrespective of the number of storing relays that are energized, only one code determining relay for a particular station can be energized during any one particular cycle of operation.

The control oflice includes a control line relay F of the neutral type. Associated with relay F is a line repeating relay FP of the quick acting neutral type which repeats each energization and de-cnergization of line relay F. A slow acting line repeating relay SA and an additional slow acting line repeating relay SAP are provided for defining the bounds of an operating cycle, that is, these relays are picked up at the beginning of each cycle and dropped at the end of each cycle. The purposes of these two relays will be more particularly pointed out in the detailed description of the operation of the system.

Associated with the line and the line repeat-- ing relays is a bank of stepping relays inciuding relays lV, 2V and 3V together with a half step repeating relay VP. These relays are pro vided to mark oil the successive steps of each cycle of operations.

Line impulsing relay POF serves to impulse the line circuit during each cycle of operations and this relay is operated in response to the step-by-step operations of the stepping relay bank by means of slow acting relay PON.

The polarity of the impulses applied to the line circuit from the line battery B is determined by a polar magnetic stick relay CS, which is controlled on each step of the cycle in accordance with the station code and the controls to be transmitted for that particular cycle.

A three position biased to neutral polar message receiving relay M is provided to repeat the balanced and unbalanced condition of the line circuit during the impulse periods of a cycle. The position of this message receiving relay each step of the cycle is stored in suitable indication storing relays LIS and EIS. EIS indicates that this relay stores the indication dur ing the early part of the impulse period of each step and LIS indicates that this relay stores the indication during the latter portion of each inrpulse period.

For the purpose of illustratingstation registration pilot relays SP1 and 21 T are used for the first step. It will be understood that in systems of such size that it requires more than one step to register the stations in the control ofiice, additional pilot relays will be connected at additional steps in the same manner as relays lPT and 2PT. These pilot relays are of the two position polar magnetic stick type although it will be understood that any suitable type may be employed. Indication receiving relays HR, and 21B are also of the two position polar magnetic stick type for storing the indications received from a transmitting field station, which field station is registered in the control office by picking up a station relay such as IST.

A starting relay STR is provided for initiating th system from the control office at the beginning of a cycle of operations for the transmission of indications. Cooperating with this starting relay is a slow acting auxiliary relay AX, the purpose of which will be pointed out in detail later in the description.

Balancing resistances a, c and d are provided for making up the Wheatstone bridge circuit. Impedance coil IlVl connected in series with resistance a is for the purpose of balancing the impedance of arm a with the impedance of arm b, the latter arm including the line circuit and the line relays. Resistance a is adjustable so that the resistance value of this arm of the bridge can be adjusted to match the resistance value of arm 19 of the bridge when the system is installed. An alternating current generator AC has been indicated in Fig. 2A, which is for the purpose of applying a momentary impulse of alternating current to the line circuit .at the beginning of a cycle of operations for picking up the starting relays at the various field stations. This generator may be of the type commonly used in telephone systems for ringing the bells connected to telephone lines, or it may be of any other suitable type such as a transformer connection to the 60 cycle commercial supply circuit.

Field station equipment.-The field station illustrated in Figs. 3A, and 3B is typical of all field stations of the system and may be adapted for use at the first, second or any other location by .merely connecting certain jumpers to arrange for the desired codes, but for convenience in the description it is assumed that this is the first station on the line by reason of the distinctive exponents employed.

A track switch TS is illustrated as operated by means of switch machine SM This switch ma chine is operated by a switch machine control relay SMR. of the two position polar magnetic stick type, governed from the control ofiice through the medium of the communication sys tem.

Suitable signals (not shown) are associated with track switch TS for governing traffic thereover and are provided with automatic signal means interrelating the traiiic over this track switch with such other sections of track and trafiic control devices as may be associated therewith. These signals are also governed from the control office through the medium of the 001m munication system by control relays such as relay SGR The control by this relay has been omitted for the sake of simplifying the present disclosure.

The illustrated track section is contemplated as being of the closed circuit type with the usual track battery and track relay which are not shown. Associated with the switch machine and the track switch is the usual switch repeating relay WP which indicates the unlocked condi-- tion and the normal or reverse position of the associated track switch.

The communication part of the system includes a line relay F of the three position biased to neutral polar type together with its quick acting repeating relay FP of the neutral. type. Slow acting relays SA and SAP are for a purpose similar to the corresponding relays in the control ofiice.

The field station includes a bank of stepping relays IV 2V 3V and the half step relay VP arranged in a similar manner and operating in synchronism with the stepping relay bank in the control office. Since the control of this bank of stepping relays is the same as the control of corresponding relays in the control office the detailed circuits at the field station are omitted, with the control being indicated by the dotted line connecting contact H]! of relay FP to the windings of these relays.

For the purpose of illustrating the selection of a station, relay S0 is shown. This relay is picked up at the beginning of a control cycle and remains up after the transmission of the station selecting code only at the station to be selected.

A resistance unit R is employed which is normally short circuited and which can be connected in the line circuit by the operation of code selecting relay CS for the purpose of unbalancing the line circuit for making up the code combinations comprising unbalanced and balanced conditions of the line.

A change relay CH is provided to register a change in any of the traffic controlling devices at the" station so that the system will be initiated for the transmission of the new indications. The operating circuits of this change relay have been omitted but it will be understood that it responds to a change in the position of the track relay, the switch repeating relay and the like by means of the momentary de-energization of its stick circuit, by the operation of these relays all of which is disclosed in Patent 1,852,402.

Lockout relay L0 is employed to determine when this field station is to transmit its indications. Whenever the lookout relay is picked up during a cycle of operations to permit the field station to transmit, the code selecting relay CS is rendered effective to be governed in accordance with the code jumpers and the positions of the various relays for applying the proper code combination to the line circuit.

Starting relay STR is provided at the field station for initiating the operation of the apparatus at this station in response to an impulse of alternating current applied to the line circuit in the control ofiice. The line winding of the starting relay is connected across the line circuit and in series with capacitor or condenser 0P This arrangement is for the purpose of preventing the normal energization of the starting relay by direct current applied at the control office, while permitting the energization of the starting relay when the control ofiice applies alternating current.

It is believed that the nature of the invention, its advantages and characteristic features can be best understood with further description being set forth from the standpoint of operation.

Operation The system of the present invention is normally in a condition of rest, from which it may be initiated into a cycle of operations either from the control ofiice or from any of the field stations whenever there are new controls or new indications ready to be transmitted. If new controls for several different field stations are ready for transmission at substantially the same time they are transmitted on separate cycles of operation, one station for each cycle. Similarly, if several stations have new indications ready for transmission at the same time they are transmitted to the control oflice, one station at a time on separate operating cycles.

It may happen that there are new controls and new indications ready to be transmitted at the same time. In such instances controls are transmitted to the required field station and simultaneously therewith indications are transmitted from that field station or some other field station during the same cycle.

Irrespective of whether a cycle is to be for the transmission of controls and/or the transmission of indications, a predetermined number of impulses are placed upon the line circuit to accomplish the step-by-step operation of the stepping relay banks in synchronism. These impulses placed upon the line circuit are time spaced, that is, they follow each other at definite time intervals. That period of time during which the line circuit is energized with an impulse is conveniently referred to as an on period, while the deenergized period of the line circuit between successive impulses is conveniently referred to as an ofi period.

When a cycle of operations is initiated for the transmission of controls, the character of the plu rality of impulses placed upon the line circuit is determined in accordance with the station to be selected and the controls to be transmitted thereto as set up by the code jumper connections and the control lever positions for that station. During a cycle of operations initiated for the transmission of indications alone, the character of the plurality of impulses applied to the line circuit is such as to prevent the selection of any station, these impulses merely causing the step-bystep operation of the control oifice stepping relay bank and the field station stepping relay bank.

When a cycle is initiated from a field station for the transmission of indications, the line circuit is conditioned by balancing and unbalancing the line at the various steps of the cycle to provide a code combination, the first part of which registers the transmitting field station in the control ofiice and the latter part of which transmits the required indications from this station to the control office. This conditioning of the line circuit is accomplished in two different portions of each on period so that the control oifice receives messages twice for each step of the system. In this way the number of indications transmitted is double the number of controls for the same number of steps because the line circuit is only conditioned for controls in a distinctive manner 1 once for each step of the cycle.

Normal conditions.- Although the system may be initiated from the field stations, the line circuit is normally deenergized by including a condenser in series with the starting relay at each field station as indicated in Fig. 1B. By referring to this figure it will be noted that no direct current from line battery B in the control ofiice can normally fiow through any of the relays connected to the line circuit because of the condensers normally connected in series with the relays which are bridged across the line circuit. This provides a convenient method for maintaining the line circuit normally deenergized, with battery potential connected to the line so that the system can be initiated from a field station by energizing this line. Likewise this provides a convenient method of starting the operation at all of the field stations when the control oilice initiates a cycle by applying a momentary impulse of alternating current to the line at the control oifice, which current will be efiective to pick up the starting relays at all field stations.

In the control ofiice relay CS is normally energized over a circuit extending from (B-), back Contact ll] of relay SA and winding of relay CS to (CN). The current flow in this circuit is in such a direction that relay CS positions its contacts to the left as indicated in Fig. 2A. Battery B is normally connected to the line circuit over a connection extending from the terminal of this battery, contact I! of relay CS in its left hand position, winding of resistance unit d, back contact it of relay SA and B line conductor. Battery B is connected to the A line conductor over a connection extending from the terminal of battery B, contact l3 of relay CS in its left hand position, winding of relay F, hack contact M of relay SA and back contact 15 of relay POF.

At the field station the track circuit is normally energized and the track relay (not shown) is normally picked up, Relay WP is normally energized with its polar contact I02 actuated to right or left hand positions for indicating the track switch in its normal or reverse locked positions respectively. Change relay CH is normally energized by a stick circuit extending through contacts of the track relay, contacts of the W1 relay and other contacts, all of which is immaterial to an understanding of the present invention but which is illustrated in Patent 1,852,402.

Manual start.With the system in a condition of rest it may be manually initiated into a cycle of operations for the transmission of controls. Whenever such a cycle is to be effected the operator first positions the control levers for the field station desired and then actuates the starting b'utton associated with that station.

Whenever the starting button for a station is actuated the result of such operation is suitably stored and if the system is in its normal condition the code determining relay for that station is immediately energized. These code determining relays for the several stations are so interlocked that if several starting buttons are actuated successively or simultaneously only one code determining relay can be picked up for any one cycle.

For the purpose of considering the operation of the present system it will be assumed that the station illustrated in Figs. 3A and 3B corresponds to starting button SB illustrated in the upper left hand corner of Fig. 2A and a detailed explanation will be given of the operation of the systern when the operator actuates button SB for selecting this station. It will be assumed that switch machine lever SML is positioned to the right as indicated in the upper left hand corner of Fig. 2B.

The operation of button SB closes a circuit for picking up relay SR which extends from contact iii of button SB and upper winding of relay SR to Relay SR closes a stick circuit for itself extending from front contact ii and upper winding of relay SR to Assuming that no other SR relay is picked up by the operation of some other starting button, a circuit is closed for picking up relay CD which extends from back contact IQ of relay POF, back contact 9 of relay SA, front contact 20 of relay SR, back contact 2| and winding of relay CD to Relay CD closes a stick circuit for itself extending from front contact 22 of relay SR, front contact 2| and winding of relay CD to In Fig. 2A it is assumed that relays SR and CD, associated with the first station in the system, are the first in the series pick up circuit extending from back contact 55 of relay POF which has just been described. The picking up of contact 28 of relay SR interrupts the circuit which leads to the next SR relay contact similar to contact 29. Therefore, although some other SR relay can be picked up the circuit for picking up its associated CD relay is not energized and cannot be energized until the end of the present cycle, when relay SR will be dropped as will be presently explained. It will thus be seen that by means of this chain pick up circuit, only one CD relay can be picked up at any one time and that will be he one nearest the live end of the series pick up circuit extending to back contact IQ of relay POF. Tl arrangement results in permitting the storof a plurality of outgoing calls and the transmission of these calls over the communication system, one at a time in an order determined by the location of the CD relays in the series.

The picking up of relay CD closes a circuit for picking up relay SA which extends from front contact 23 of relay CD, back contact 24 of relay lV, back contact 25 of relay VP and winding of relay SA to The picking up of relay SA closes a circuit for picking up relay SAP which extends from front contact 25 of relay SA and winding of relay SAP to Since relay SAP is relatively slow in picking up its contacts, a circuit is closed after relay SA picks up its contacts and before relay SAP picks up its contacts for energizing the line circuit with alternating current. This circuit extends from the lower terminal of the alternating current source AC, back contact 21 of relay PON, back contact 28 of relay SAP, front contact l2 of relay SA, B line conductor, back contact B3 of relay SAP ,'upper winding of relay STR condenser CP A line conductor, back contact I of relay POF, front contact M of relay SA, back contact 29 of relay SAP and back contact 30 of relay PON to the upper terminal of the alternating current source AC. This momentary application of alternating current to the line circuit is effective to pick up relay STR at the first field station. Since the starting relays'at the other stations, such as S'IR and S'I'R of Fig. 1B, are likewise connected across the line circuit in series with condensers CP and CP these starting relays will also be picked up.

The picking up of relay STR closes a stick circuit for itself extending from back contact H14 of relay SAP front contact 105 and lower winding of relay S'IR to It will be understood that the other starting relays at all other stations close similar stick circuits for themselves.

Referring back to the control ofiice, the picking up of contact Ill of relay SA disconnects relay CS from (13-) and connects it to the polarity selecting circuit extending through contacts of the stepping relays. It will be assumed that the sta tion illustrated in Figs. 3A and 3B responds to a station selecting code Therefore the polarity of the first impulse is determined when relay SA picks up its front contact it because the circuit for actuating relay CS extends to (3+) through the first code jumper. This circuit arrangement for selecting the polarity of each impulse will be explained in detail later. At present, however, it will be understood that during the conditioning off period (when the line circuit is not energized with direct current because relay SAP at the end station indicated in Fig. 1C is not picked up) the CS relay positions its contacts H and i3 for energizing the line circuit during the succeeding on period with the proper polarity as selected by the particular CD relay which is picked up.

Referring to the field station, the picking up of relay S'IR closes a circuit for picking up relay SO which extends from (CN), back contact I05 of relay SA front contact ID! of relay S'IR and lower winding of relay S0 to (B). It will be understood that the SO relays at all other stations are picked up over similar circuits.

The picking up of relay STR closes a circuit for picking up relay SA which extends from front contact I08 of relay STl-t and winding of relay SA to During the impulsing of the line circuit, relay FP intermittently closes its front contact I09 at such a rate that relay SA does not have time to drop between impulses. As long as relay SA is picked up an energizing circuit is closed for relay SAP which extends from front contact II 0 of relay SA and winding of relay SAP t0 Similar circuits are closed at all other stations for picking up the SA and SAP relays at these stations. The picking up of relay SAP at the end station closes its front contact 390 for connecting the two line conductors together, which provides a closed circuit path for direct current from battery B in the control oflice.

It will be noted that when alternating current is applied to the line at the beginning of the cycle as just described the line relays at the field stations are not included in the line circuit. This is because they are normally short circuited. Line relay F is short circuited at back contact I I I of relay SAP and the other line relays at the other stations are likewise normally short circuited. This is to prevent the undesired operation of the line relay contacts when alternating current is applied to the line. The alternating current is disconnected from the line when relay PON is energized (see Fig. 2A) over a circuit extending from front contact 3I of relay SA, back Contact 32 of relay 3V, back contact 33 of relay 2V, back contact 34 of relay IV, back contact 35 of relay VP and winding of relay PON to Since relay PON is picked up before the SAP relays at the field stations pick up, this impulse of alternating current does not energize any of the line relays.

The picking up of relay SAP marks the end of the conditioning off period and the beginning of the first on period, since the line is now energized by direct current over a circuit extending from the terminal of battery B, contact I3 of relay CS in its right hand dotted position (actuated to this position as will be later described), winding of relay F, front contact 29 of relay SAP, front contact I4 of relay SA, back contact I5 of relay POF, A line conductor, winding of relay F contact II2 of relay CS in its neutral position, the line relays and similar contacts at other stations in series, winding of line relay F at the end station, front contact 390 of relay SAP through the other stations in series, front contact I03 of relay SAP B line conductor, front contact I2 of relay SA, front contact 28 of relay SAP, resistance unit d and contact I I of relay CS in its right hand dotted position to the terminal of battery B. Current flowing in this circuit picks up all of the line relays, including relay F in the control office.

The picking up of front contacts 36 and 31 of relay SAP and the front contact 38 of relay F connects resistance units 0 and a in the line circuit to make up the Wheatstone bridge. By transposing the different relays, impedance coils and resistance units from Figs. 2A and 3A to Fig. 1A it will be found that the line circuit is made up as indicated in Fig. 1A, with the line and the line relays in arm b of the bridge and with battery B and relay M at opposite conjugate points of the bridge. As long as arm I; of the bridge balances arm a so that the product of the resistance values in arms, a, d equals the product of the resistance values in arms b, c, the terminals of relay M are connected at points of equal potentialwith respect to battery B and no current flows through this relay. This balanced condition can be obtained when the system is installed by adjusting the value of resistance a to balance the value of the resistance made up by the length of the line circuit, plus the resistance of the line relays in the system.

Impuising of the line is effected by Opening back contact I5 of relay POF and since this contact is located at point X (with the reference nu meral I5 associated therewith) in Fig. 1A and since the dropping of relay F when the line is so impulsed opens the circuit of relay M at its front contact 38 (which is located at point X marked with reference numeral 38 in Fig. 1A), it will be seen that relay M is not actuated when the line circuit is energized and de-energized. Relay POF, closing its contact I5, establishes the balanced condition to prevent current flowing through the branch which includes relay M before line relay F closes its front contact 38 to connect relay M in this branch. The manner of unbalancing the bridge for operating relay M to receive indications will be explained later. From the above it will be seen that relay M is not energized during the impulsing of the line circuit unless something takes place to unbalance arm b of the bridge. This is true irrespective of the direction of the energization of the line circuit from battery B, because relay M is connected at points of equal potential irrespective of the direction of current fiow in the Wheatstone bridge circuit. Polarity selection of impulses-Whenever the system is initiated from the control ofiice the first impulse applied to the line circuit is an impulse of alternating current as above described. When relay SAP at the end station picks up, following the application of this alternating current impulse, the line circuit is energized with direct current over the circuit previously described. This first energization of the line circuit, conveniently referred to as the first onperiod, is in character, that is, the terminal of battery B is connected to the A line conductor which includes the line relays. This impulse is because relay CS actuates its polar contacts to their right hand dotted positions during the conditioning period preceding the first on period. Relay CS is actuated to the right during the conditioning off period by means of a circuit extending from (B+) code jumper 39, front contact 40 of relay CD, code bus AI, back contacts 42, 43 and 44 of relays IV, 2V and 3V respectively, front contact ll! of relay SA and winding of relay CS to (CN).

This application of energy to the line circuit causes various relay operations but for the time being these operations will be omitted, it being assumed that after a predetermined time the line circuit is de-energized to mark the beginning of the first off period by the operation of relays PON and POF. Such de-energization of the line circuit results in the energization of the first stepping relay IV. The picking up of relay IV opens back contact 42 and connects relay CS to code bus 4'5 through front contact 42. In this case code bus 45 is energized in accordance with the position of code jumper 41 because relay CD is energized.

In the event that code jumper 39 is connected to (3-) in its dotted line position, then relay CS is actuated to its left hand position for applying a impulse to the line circuit. In the following explanation of the operation of the CS relay it will be understood that the connections of the code buses by way of front contacts of relay CD and the code jumpers or the lever contacts to opposite terminals of the battery from that indicated at the respective steps, positions relay CS to the opposite position from that described for applying an impulse of opposite polarity to the line circuit as will be readily understood.

When relay IV is picked up during the first off period a circuit is closed for actuating relay CS to its left hand position extending from (B--), code jumper 41, front contact 48 of relay CD, code bus 45, front contact 42 of relay IV, back contacts 43 and 44 of relays 2V and 3V respectively, front contact I0 of relay SA and winding of relay CS to (CN) With the contacts of relay CS in left hand positions, battery B is connected to the A line over a circuit extending from the terminal of battery B, contact I3 of relay CS in its left hand position, winding 0 of relay F, front contact 28 of relay SAP, front contact I4 of relay SA, back contact I5 of relay POF, A line conductor and over the remainder of the line circuit previously described, to the terminal of ba tery B byway of contact II of relay CS in its left hand position. It will be noted that the control of relay 'CS is effected upon the picking'np of the stepping relay during each of? period, so that when the next on period begins by the closing of back contact I5 of relay POF, battery B is connected to the linein the proper direction and this connection is not changed during this on period, but the next change takes place during the next oiT period. After the second impulse has been applied to the line circuit for a predetermined period of time, the line is again opened by the picking up of back contact I5 of relay POF. This de-energization of the line circuit causes the second step to be taken by energizing relay 2V. Relay CS is then connected through front contact 43 of relay 2V to code bus 46 which extends through front contact 49 of relay CD to lever SML. Relay CS will he energized in accordance with the position of lever SM].- and as indicated in Fig. 23 this energization is effected by a (3+) polarity for actuating relay CS to the right. This means that the line circuit will be energized with a impulse during the next on period.

This operation occurs on each step of the cycle so that relay CS is energized in accordance with the polarity applied to the respective code buses for each step. During the first part of each operating cycle the code buses for the corresponding steps are energizedwith or Aptialsmaccordance with the character of the code for the desired station. During the latter part of the operating cycle the code buses are energized in accordance with the positions of the control levers for the selected station.

It has been explained that code bus 46 is energized in accordance with the position of lever SML. In a similar manner code bus 56 (and additional code buses when required) will be energized over circuits extending through front contacts of relay CD to other levers, such as a signal control lever or the like.

From the above it will be seen that the impulses applied to the line circuit always begin with a short application of alternating current to the line for a control cycle, while the following impulses are of positive or negative direct current depending upon the code jumpers and control levers rendered efiective by the particular code determining relay which is picked up for that particular cycle. Also that polarity determination is accomplished by relay CS having the polarity of its energization established so that it takes its position while the line circuit is de-energized.

Operation of stepping relays-Irrespective of the particular polarity with which the line circuit is energized the line relays are effective to operate the line repeating relays FP (with suit able exponent) each time the line circuit is energized. For example, relay F closes a circuit for operating relay FP extending from front contact SI of relay F, front contact 52 of relay SA, back contact 53 of relay AX and winding of relay FP to At the field station the closure of contact H3 of relay F in either its right or its left hand position closes an obvious energizing circuit for relay FP.

At the beginning of the transmitting part of the cycle, marked off by the picking up of relay SAP in the control office, a circuit is prepared for picking up half step relay VP at the beginning of the first on period. This circuit extends from front contact 54 of relay SAP, front contact 55 of relay FP, back contact 56 of relay IV and winding of relay VP to The picking up of relay VP closes a stick circuit for itself extending from front contact 54 of relay SAP, front contact 51 ,of relay VP, back contact 53 of relay IV and winding of relay VP to When relay FP is dropped during the first off period a circuit is closed for picking up relay IV which extends from front contact 58 of relay SAP, back contact 59 of relay front contact 60 of relay VP. back contact SI of relay 2V and winding of relay 1V to Relay IV closes an obvious stick circuit for itself at its front contact 82. Before relay IV opens its back contact 56 a second stick circuit is provided for relay VP which extends from front contact 54- of relay SAP, back contact 55 of relay FP, front contact 53 and winding of relay VP to When relay FF is picked up during the second on period, relay VP is dropped because its first described stick circuit is open at back contact 55 of relay IV and its second stick circuit is open at back contact 55 of relay FP.

Relay 2V is picked up in the next off period when relay FP drops its back contact 59, over a circuit extending from front contact 58 of relay SAP, back contact 59 of relay FP, back contact 60 of relay VP, back contact 64 of relay 3V, front contact 65 of relay IV and winding of relay 2V to Relay 2V closes an obvious stick circuit for itself at its front contact 85.

During the third on period the picking up of relay FP closes a circuit for picking up relay VP which extends from front contact 54 of relay SAP, front contact 55 of relay FP, back contact 61 of relay 3V, front contact 68 of relay 2V and winding of relay VP to Relay VP establishes its stick circuit as before.

During the succeeding "off period the dropping of relay FP closes a circuit for picking up relay 3V which extends from front contact 58 of relay SAP, back contact 59 of relay FP, front contact 60 of relay VP, front contact SI of relay 2V and winding of relay 3V to Relay 3V closes an obvious stick circuit for itself at its front contact 69.

During the fourth on period the picking up of relay FP de-energizes relay VP because its first stick circuit is open at back contact 51 of relay 3V and its second stick circuit is open at back contact 55 of relay FP.

Since the fourth impulse is the last one of the cycle the next de-energization of the line is effective to return the system to normal. This is because relay POF is not dropped for a reason to be later explained so that the line is de-energized for a comparatively long interval of time. This effects the de-energization of relay SA by the extended opening of front contact 10 of relay FP. Relay SA drops its front contact 26 and after a comparatively long interval of time relay SAP is released. The dropping of front contact 58 of relay SAP de-energizes the stick circuits of the stepping relays and they are released. In the event that the system makes use of an odd number of steps, then relay VP will be picked up when the system is to be restored to normal and in such event the dropping of front contact 54 of relay SAP de-energizes the circuit of the VP relay.

It is to be understood that these circuit connections may be extended for as many steps as desired, with alternate stepping relays closing and opening the various circuits in the same manner shown in connection with the three illustrated relays of the stepping bank. Since the operation of the stepping relays at the field stations is the same as described in connection with the control office a description of this operation will be omitted, since the detailed circuits of the stepping bank at the illustrated field station have not been shown. It should be noted however, that the stepping at the field station is dependent upon relays SAP and FP only. This means that all stations will step through a cycle irrespective of whether a station is selected or dropped out during this cycle. The reason for this is to maintain the line circuit in a balanced condition and since this condition is established with the line relays of all stations in the circuit it is necessary that these relays be kept in the circuit throughout the cycle. It is obvious that this is accomplished because relay SA is picked up in response to the operation of relay S'lR by the alternating current impulse applied to the line and relay SA picks up relay SAP to include relay F in the line circuit by opening back contact III. Since relay F directly controls relay FP the control of the stepping relay bank is efiected independenta JiVls up there is no circuit for energizing relay of the station selecting relay S This same discussion of course applies to the otherfield stations in the system since the impulse of alternating current is effective to pick up the STR relays at all stations.

Impulsing of line circuit-The picking up of relay VP during the first on period as above described opens the energizing circuit of relay PON at back contact 35. It has already been described how relay PON is picked up during the conditioning period. After a predetermined interval of time relay PON drops its contact II which closes a circuit for picking up relay POF extending from front contact I2 of relay VP, back contact II of relay PON and lower winding of relay POF to The picking up of relay POF opens the line circuit to mark the beginning of the first off period. During this off period relay IV, is picked up as already described and a circuit is closed for picking up relay PON which extends from front contact 3| of relay SA, back contacts 32 and 33 of relays 3V and 2V respectively, front contacts 34 and 35 of relays IV and VP respectively and winding of relay PON to The picking up of back contact II of relay PON de-energizes relay POF. The dropping of relay POF energizes the line circuit to mark the beginning of the second on period. During this period relay VP is dropped and the dropping of its front contact 35 de-energizes relay PON. The dropping of relay PON closes a circuit for picking up relay POF which extends from front contact I8 of relay IV, back contact II. of relay PON and lower winding of relay POF to The picking up of back contact I5 of relay POF de-energizes the line circuit to mark the begining of the second off period. During this ofi period relay 2V is picked up which closes a circuit for picking up relay PON extending from front contact 3i of relay SA, back contact 32 of relay 3V, front contact 33 of relay 2V, back contact 35 of relay VP and winding of relay PON to The picking up of back contact II of relay PON de-energizes relay POF.

The dropping of relay POF closes its back contact i5 which energizes the line circuit to mark the beginning of the third on period. During this on period relay VP is picked up 3 which opens the energizing circuit of relay PON at back contact 35. The dropping of back contact ii of relay PON closes the previously described pick up circuit for relay POF.

The picking up of relay POF opens its back 40 contact I5 which de-energizes the line circuit to mark the beginning of the third of period. During this period relay 3V is picked up which closes a circuit for picking up relay PON extending from front contact 3| of relay SA, front contact 32 of relay 3V, front contact 35 of relay VP and winding of relay PON to The picking up of back contact 'II of relay PON, de-energizes relay POF.

The dropping of relay POF energizes the line o circuit at its back contact I5 to mark the beginning of the fourth on period. During this on period relay VP drops and at its frontcontact 35 opens the energizing circuit of relay PON. Relay PON drops its back contact II to close the pick up circuit for relay POF.

' The picking up of relay POF marks the beginning of the change to normal or last off period. Since relay VP is down and since relay PONmtifiwhich results in'relay POF re- .60 maining energized for a marativeiy lcmg interval of time because its energizing circuit is closed at front contact I8 of relay IV and back contact II of relay PON.

Relays F and FF remain down for a suflicient interval of time to drop relay SA and thereafter relay SAP is dropped as previously described. Since the line relays and their repeating relays at the various field stations likewise remain down for a comparatively long interval of time, the slow acting relays at these stations are de-energized and the system is returned to its normal condition. 7

In this connection it will be noted that another oifice for operating the stepping banks at the various stations in synchronism with the stepping bank in the control office. This combination of impulses is provided because relay CS is not selectively actuated when no CD relay is picked up. In other Words, relay CS being actuated to the left at the start of a cycle as previously described remains in this position throughout such an indication cycle so that all impulses applied to the line circuit are This corresponds to a phantom code which is not assigned to any station so that the transmission of such a code is not effective to select any station for the transmission of controls when the system is operating through a cycle for the transmission of indications alone.

Transmission of controls-Assuming that the proper code combination is applied to the line circuit for selecting the station illustrated in Figs. 3A and 3B, then upon the application of the third impulse to the line circuit (the character of which is determined in accordance with the position of lever SML in the control office) the switch machine control relay SMR is energized from (18+) or (B-) depending upon the character of the impulse applied to the line circuit. With lever SML in its right hand position a impulse will be applied to the line circuit and potential will be connected to relay SlVlR over a circuit extending from (B-]-) contact I23 of relay F in its right hand dotted posi tion, front contact 1124 of relay S0 winding of relay SMR back contact I25 of relay 3V front contacts H9 and H5 of relays 2V and IV respectively, front contact N4 of relay S0 and front contact I66 of relay SA to (CN). In the event that lever SML is in its left hand dotted position a negative impulse is applied to the line circuit resulting in connecting (B) through contact I23 of relay F in its left hand dotted position over the above described circuit. Thus polar contact I25 of relay SMR assumes a position corresponding to lever SML for actuating the switch machine to a normal or a reverse position over local circuits which are obvious.

In a similar manner any number of additional steps may be provided for transmitting additional controls to this field station for governing the signals and such other devices as may be necessary.

End of cycZe.It has already been explained how most of the relays in the control ofilce are restored to their de-energized positions at the end of an operating cycle. The continued deenergization of the line circuit is sufficiently long to drop relays SA and SAP in sequence at the field station. The dropping of front contact Hit of relay SAP de-energizes the stepping relays and the dropping of front contact 5% of relay SA de-energizes the station selecting relay. The dropping of the other contacts of the SA and SAP relays restores the line circuit to its normal condition. Of course similar operations are effected at all other field stations.

In the control oflice, relay SR is dropped when relay VP drops in the on period following the third off period during which relay 3V picks up. Relay SR is die-energized by means of a circuit extending from front contact ll of relay 3V, back contact iii of relay VP, front contact is of relay CD, front contact 8 and lower winding of relay SR to The dropping of front contact 22 of relay SR de-energizes relay CD.

Transmission of indications.Although this system is of the coded duplex type arranged for the transmission of indications from any station to the control office during the same cycle that controls are transmitted to the same or some other station, it will first be explained how the system operates for the transmission of indications alone on a separate operating cycle. The duplex feature of the system will be explained later in the description.

There may be trains in various portions of the territory supervised by the operator and these trains may enter or leave the track sections at two or more points at substantially the same time. Similarly the switches and signals at the various locations may be operated in such a way by the operator that several of these traffic controlling devices assume new conditions at substantially the same time. Therefore some means must be provided to allow only one field station to transmit at any one time to avoid mutilation of the registration of the code calls and to avoid the transmission of false indications.

The arrangement for allowing the field stations to transmit only one at a time in a predetermined sequence will be explained in connection with the look-out feature, following the description of the operation of the system with respect to the transmission of indications from a single field station, assuming that such station is the only one having new indications to transmit at the beginning of the cycle.

Automatic start from a field station.-Referring to Fig. 3A of the accompanying drawings, a change in the condition of the detector track section or a change in the condition of the other traffic controlling devices at this station may occur at any time for dropping the normally energized change relay CH It will be understood that the changes in various devices at the station effect the de-energization of relay CH by momentary d e-energizing its stick circuit, all of which is familiar to those skilled in "the art and is immaterial to the understanding of the present invention.

When relay CH drops its back contact till a circuit is closed for picking up relay L0 which extends from the terminal of battery B in the control oiiice which is connected to the A line conductor, back contact MS of relay 8A back contact E2? of relay CH upper winding of relay L0 impedance 1M back contact me of relay SAP and over the B line conductor to the terminal of battery B in the control oflice. Since this circuit includes the winding of relay F in the control oflice this relay is picked up to close a circuit for picking up relay STR which extends from front contact 5! of relay F, back contact 52 of relay SA and upper winding of relay STR to Relay STR closes a stick circuit for itself extending from front contact 13 and upper winding of relay STR to Relay STR closes a circuit for picking up relay SA which extends from front contact M of relay STR, back contacts 2-. and 25 of relays !V and VP respectively and winding of relay SA to Relay STR also closes a circuit for picking up relay AX which extends from back contact 5d of relay SAP, front contact 15 of relay STR and winding of relay AX to The picking up of back contacts 53 and iii of relay AX opens the circuits of relays FF and M, so that these relays cannot be picked up during the conditioning period of a cycle initiated from a field station. This is to prevent stepping taking place in the control oflice and also to prevent relay M falselv re istering an indication at this point of cycle cannot be started until relay POF is dropped and this occurs after the stepping relays are dropped by the dropping of relay SAP. In other words the dropping of front contact IQ of relay W (or front contact 12 of relay VP if the number of steps is such that relay V? is up) de-energizes relay PCB and shortly thereafter it drops its contacts. This means that the dropping of relay POF is the last operation of the cycle and since the pick up circuit for the CD relays extends through back contact 59 of relay POF, another cycle cannot be started until this latter relay is restored to normal.

Station selection for comirols.When controls are to be transmitted from the control oflice the field stations are selected one at a time in accordance with the combination of and impulses applied to the line circuit during the first or station selection part of the cycle. As above pointed out, each impulse applied to the line circuit causes the step-by-step mechanism at the control office and at each field station to take one step irrespective of the polarity of impulses. Since the polarity of each impulse may be made either or the number of code combinations obtained is equal to two raised to the power of the number of steps. In other words, two steps gives four different combinations, 3 steps gives 8 different combinations, e steps gives 16 different combinations and each additional step doubles the number of possible distinctive codes provided. In the present en bodiment it is assumed that the number of stations is such that they may be selected on two steps of the cycle.

The circuits for each field station are similar, the only difference being in the positions of the station code jumpers shown in Fig. 3A, which jumpers serve to condition or energize one or the other of the two station selection buses indicated bus and bus in accordance with the code call assigned to that particular station. The transmission of a code call connects a selecting stick circuit of a station selecting relay S to one or the other of these station selecting code buses. If the code call transmitted corresponds to the code call assigned to the station then the selecting stick circuit will be connected to an energized bus for each step. If the trans mitted code call does not correspond to the station code call then this selecting stick circuit will be connected to a de-energized bus at one step thereby causing the corresponding station se ecting relay S0 to be de-energized. The station with which communication is held is the one at which the station selecting relay remains energized, all other stations except this one having been dropped out during the station selecting part of the cycle.

More specifically considering the operation of Fig. 3A, the application of the first impulse to the line circuit was as previously described which is effective to close the selecting stick circuit for energizing relay S0 during the first on period over a circuit extending from (CN), front contact I65 of relay 8A front contact N4 of relay SO, back contact H5 of relay 1V code jumper H5, bus, contact ii"! of relay F in its right hand clotted position and lower winding of relay S0 to (B). It will be understood that back contact H8 of relay W is picked up at this time so that the selecting stick circuit of relay S0 is dependent upon the above described circuit through jumper 555 only. It will also be recalled that relay S0 at this station (and similar relays at all other stations) were picked up when relay S'IR closed its front contact lll'l at the beginning of the cycle.

During the off period which follows the first on period relay F restores its contact l l! to its neutral position which closes a stick circuit for relay SO extending from (CN), front contact m6 of relay SA front contact H4 of relay S0 contact Ill in its neutral position (which makes its neutral position contact before breaking its actuated position contact) and lower winding of relay S0 to (B). As soon as relay FP drops its back contact H8, contact ll! of relay F is shunted to provide the above described stick circuit through cont-act H8. The purpose of contact l H is to make up this stick circuit before the selecting stick circuit is broken at the time relay F drops its contacts.

During the second on period a selecting stick circuit is closed for relay S0 extending from (CN) front contact I96 of relay SA front contact N4 of relay S0 front contact H5 of relay [V back contact H9 of relay 2V code jumper I20, bus, contact H! of relay F in its left hand dotted position (because the second impulse is and lower winding of relay S0 to (B).

Thus the selecting stick circuit of relay S0 is energized or de-energized during each "on period depending upon whether the polarity of the received impulse connects this selecting stick circuit to the particular or bus which is energized in accordance with the code jumper connections. During each 01f period following an on period which energizes the selecting stick circuit of relay S0 this relay is maintained energized over the stick circuit including contact ll! of relay F in its neutral position and back contact I N3 of relay FP as already described.

At half of the stations code jumper H6 is connected in an active position while at the other half of the stations it is connected in an inactive position. Thus with the first impulse a certain half of the stations will be selected by maintaining the SO relays energized at the stations, but if the first impulse is the other half of the stations will be selected by maintaining the SO relays at these stations energized. This selection continues throughout the station selection steps for as many steps as required until the station selecting relay is energized at only one station, which is the station that will receive a code call to operate the particular controls at this station.

This scheme of selection may be said to be upon the sub-division or elimination basis, since all of the station selecting relays are energized at the beginning of a cycle and half de-energized upon the first step, with half of those remaining de-energized upon the second step and so on until the SO relay at only one station remains picked up. In the present disclosure it is assumed that the station is selected during the first two steps of the cycle with relay 1V down and with relay 1V picked up. When relay 2V is picked up in the off period following the second impulse a permanent stick circuit is closed for sticking relay SO during the remainder of the cycle which extends from front contact |2| of relay 2V front contact 122 and upper winding of relay S0 to Ihe transmission of indications and the registration of a station at the control office during a cycle when no controls are transmitted, which will be later described, is effective to transmit a combination of all impulses from the control the cycle by picking up indication storing relay EIS before the system is ready for this relay to be picked up.

The picking up of relay SA closes the previously described pick up circuit for relay SAP. The picking up of relay SA also disconnects battery B from the line circuit at back contacts l2 and i i and connects the alternating current generator to the line circuit over a circuit including back contacts 21 and 39 of relay PON, back contacts 28 and 29 of relay SAP and front contacts i2 and M of relay SA. The removal of the battery connection from the line circuit drops relay F but since relay AX was picked up this first operation of relay F is ineffective to operate its repeating relay FP.

The alternating current impulse applied to the line circuit is effective to pick up relay STR at the calling station, since the current applied to the A line conductor finds a path through condenser CP upper winding of relay STR and back contact 103 of relay SAP to the B line conductor. Relay STR closes a stick circuit for itself by way of its previously described stick circuit. Since the line circuit extends through the calling station illustrated in Fig. 3A all other starting relays will be picked up and all other stations will be started in operation in the same manner as previously described in connection with a control cycle.

Impedance Ill/l connected in series with the upper Winding of L0 is of such a resistance value that it does not interfere with the proper opera.- tion of relay L0 from the direct current source applied to the line circuit, but this impedance unit has such an impedance value that the alternating current applied to the line circuit for picking up the starting relays is not effectively shunted by means of the bridge across the line which includes this impedance unit. In other words 1M is of low resistance and high impedance. This impedance unit also is effective to prevent sufficient current from the alternating current source flowing through the upper winding of relay LO to kick this relay down. Relay L0 is stuck up at this time over a circuit extending from back contact I30 of relay SA back contact [3! of relay SAP front contact I32 and lower winding of relay L0 to When relay SAP in the control office picks up its back contact 54, relay AX is de-energized to connect relays M and FP to their operating circuits. When relay SAP at the end station is picked up and relays SA and SAP in the control oflice are picked up, the line circuit is established and the line relays at all stations as Well as line relay F in the control ofiice are picked up. As above mentioned relay L0 is stuck up over a circuit including back contact E36 of relay SA Before relay SA picks up to open this stick circuit direct current is applied to the line conductors. This direct current supplies energy for holding relay L0 over a circuit extending from the A line conductor, front contact i253 of relay L0 back contact i 2"! of relay CH upper winding of relay L0 impedance 1M and back contact 83 of relay SAP tothe B line conductor. Therefore after relay SA opens its back contact I30, relay L0 at the calling station is maintained energized by way of its upper winding until relay SAP picks up its back contact N33 to open this upper winding. Since back contact N33 is of the follow-up type it is not opened until the stick circuit of relay L0 is again established through front contact I 30 of relay SA and front contact i3! of relay SAP With the stick circuit of relay L0 again established it is maintained in its energized condition until the end of the cycle.

The picking up of back contact iii of relay SAP removes the shunt from relay F and the picking up of front contact 3% of relay SAP at the end station places the system in condition for stepping through the cycle. The step-bystep operations are effected in the same manner as already described in connection with a control cycle. It will thus be seen that the initial alternating current impulse is applied to the line in connection with an indication cycle for starting all stations and that all stations step through the cycle in synchronism.

Since it is assumed that there are no controls to be transmitted, relay CS in the control office remains in its left hand position throughout the cycle for applying a series of impulses to the line circuit. This series of impulses makes up a phantom code combination which is not used for selecting any station for controls. Relay STR is de-energized by means of a circuit which extends from (-1-), front contact "ii of relay 3V, back contact 78 of relay VP, front contact 86 and lower winding of relay STR to This circuit is effective to ole-energize relay STR because it energizes its lower winding in opposition to its energized upper winding. This circuit for kicking down relay STR is effective near the end of the cycle after its contacts i i and "i5 are of no more use during this cycle. Relay SA is maintained energized during the stepping operations by means of a circuit extending through front contact iii of relay FP.

Registration of a field station.-At the particular field station. (assumed to be the station illustrated in Figs. 3A and 33) having indications to transmit, the lock-out relay is energized throughout the cycle as previously explained. Assuming that the stepping relay bank at the control oflice operates in synchronisrn with the stepping relay banks at all field stations for reasons previously described, it will be noted that the closure of front contact I33 of relay L0 applies potential to contact E36 of relay F for energizing relay CS at the various steps of the cycle. Since no contact similar to E33 at any other station is picked up the operation of the line relays at these other stations is ineffective to condition their code selection relays similar to relay CS During the first part of the first on period relay CS is picked up over a circuit extending from code jumper I35, bus iE back contact I35 of relay 5V back contact 537 of relay VP winding of relay CS contact I36 of relay F in its actuated position and front contact I33 of relay L0 to It will be mentioned at this point that relay CS at the field station and relay M in the control office are of the biasedto-neutral polar type for speed of operation only.

The picking up of relay CS opens its contact iii. which inserts resistance R in series with the line circuit to unbalance the line by increasing the resistance value of arm 17. By referring to Fig. 1A it will be seen that this unbalanced condition of the Wheatstone bridge circuit is effective to allow current to flow through the Wind-- ing of relay M for operating this relay. Relay M picks up its contact 8i which closes a circuit for picking up relay EIS extending from contact iii in its actuated position, back contact 82 of relay 3V, back contact 33 of relay 2V, back contact 84 of relay iV, back contact 85 of relay ill) VP, and upper winding of relay EIS to Relay EIS closes a stick circuit for itself extending from front contact 86 of relay F, front contact 8! and lower winding of relay EIS to In the event that code jumper I35 of Fig. 3B is disconnected from by being in its dotted line position, then relay CS is not energized and resistance R is not inserted in the line circuit. This results in the Wheatstone bridge circuit remaining in balance so that relay M is not energized. With relay M de-energized relay B18 is not picked up. This indicates the selection of two indications during the early portion of the first on period.

The VP relays have been indicated as being slightly slow to pick up and slow to release in order to provide a little more time for actuating relay CS in the early part of the on period and for registering this indication by picking up relay EIS in the early part of the on period. After relay VP at the field station is picked up the condition of the late portion of the on period is transmitted. More specifically a circuit is closed from jumper I38, bus IL back contact I39 of relay IV front contact I37 of relay VP winding of relay CS contact I3 of relay F in its actuated position and front contact I33 of relay L0 to Relay CS is picked up to again unbalance the bridge circuit for causing relay M to be picked up after relay VP in the control office is picked up. A circuit is now closed for picking up relay LIS which extends from contact 8! of relay M in its actuated position, back contacts 32, 8S and 84 of relays 3V, 2V and IV respectively, front contact 85 of relay VP, back contact 88 of relay PON and upper winding of relay LIS to Relay LIS closes a stick circuit for itself extending from front contact 86 of relay F, front contact 89 and lower winding of relay LIS to It will be obvious that with jumper I38 disconnected from relay CS is not energized, relay M is not picked up and the circuit for picking up relay LIS is not completed.

When relay POF is picked up to terminate the first on period and before relay FF is dropped, circuits are closed for executing the indications received and stored on relays EIS and LIS. Since it is assumed that relay EIS is picked up the closure of front contact 98 of relay POF establishes a stick circuit for relays EIS and LIS which is effective after relay F drops its front contact 88 and until relay PON picks up its back contact 9!. Therefore the actuated storing relay or relays will be stuck up during the succeeding off period until the indication stored by these relays is executed. In the example assumed a circuit is closed from (13+), front contact 82 of relay EIS, front contact d3 of relay FP, front contact 84 of relay POF, back contacts 95, 96 and 81' of relays 3V, 2V and IV respectively, bus IE and winding of relay IPT to (CN). This circuit is effective to actuate the polar contact of relay IPT to the right.

A circuit is closed from (13+), front contact 98 of relay LIS, front contact GS of relay FP, front contact 26! of relay POF, back contacts 292, 283 and 204 of relays 3V, 2V and IV respectively, bus IL and winding of relay ZPT to (CN). Current in this circuit is effective to position the polar contacts of relay ZPT to the right.

In the event that relay EIS is not picked up, then the above described circuit extending to relay IPT is from (3-) at back contact 92 of relay EIS for positioning relay IPT to the left.

Similarly if relay LIS is not picked up the circuit for relay ZPT extends from (B) at back contact 98 of relay LIS for actuating relay 2PT to the left. It is now obvious that storing relays EIS and LIS store the indications at the various steps of the cycle as selected by the stepping relay contacts in a similar manner to that described for the first step.

Since it is assumed that station registration is accomplished during the first on period, the pilot relays IPT and ZPT being positioned to the right as above explained close a circuit for picking up the No. 1 station relay IST after relay IV is actuated during the succeeding off period. This circuit extends from front contact 265 of relay IV, contact 286 of relay IPT in its right hand position, contact 28'! of relay 'ZPT in its right hand position, conductor EL and winding of relay IST to This conductor is indicated EL because it refers to the fact that g the line circuit when unbalanced in both the early and late on periods of the cycle energizes this conductor.

If the line circuit is only unbalanced in the early portion of the on period because code jumper I35 of Fig. 3B is connected to and code jumper I38 is disconnected from then relay EIS will be picked up for positioning relay IPT to the right and relay LIS will remain down for positioning relay 2PT to the left. This condition extends the circuit from front contact 205 of relay IV to early conductor E which leads to another station relay. With jumper I35 disconnected from and jumper I38 connected to the above condition is reversed, so that relay IPT is actuated to the left and relay ZPT is actuated to the right for energizing late conductor L only. The condition of the line remaining balanced during both portions of the on period corresponds to a phantom code, because this is the condition which exists when controls are transmitted alone and since no station must be registered in the control ofiice under this condition the conductor selected by relay IPT and ZPT in their left hand positions is the phantom conductor and does not connect to any station relay.

It is believed that the above example indicates that four different code combinations or selections are made on one step, three of which may be used for registering three stations. On two steps 16 different code combinations are made up, 15 of which may be used for station registration with the sixteenth corresponding to the phantom code.

After the record set up on the storing relays has been executed these relays are de-energized in the next off period by the picking up of back contact SI of relay PON. At the field station the CS relay is de-energized during the succeeding off period (when energized by a late indication such as code jumper I38) by the dropping of contact I34 of relay F Therefore the resistance R is removed from the line circuit when the line is de-energized so that the balanced condition will be established at the beginning of the next on period. It will be noted that relay M is not included in the circuit until relay F picks up its front contact 38 and until relay POF drops its back contact 6. This provides a means for allowing the line circuit to reach a stable condition before relay M is connected to the line.

In connection with the transmission of indications as above described it will be obvious that same number of indication conditions as there are control conditions for a given period of time, by omitting the late indication buses of Fig. 33 such as IL 2L 3L and 4L and also omitting late indication storing relay LIS and the circuits for controlling and controlled by this relay.

Transmission of indications.After thus having registered the particular station in the control office having indications ready to transmit the remaining steps of the cycle are employed for the transmission of those indications. As above mentioned the line circuit is conditioned during the on periods by unbalancing or leaving balanced the Wheatstone bridge circuit of which the line circuit forms one of the arms.

For example, when the line circuit is energized for the next on period following the station registering steps, relay F closes its contact I34 and, assuming relay WP to have its contacts in the positions shown in Fig. 315, a circuit is closed from front contact Hill of relay WP contact Hi2 of relay WP in its right hand position, bus 2L back contact Mi of relay 2V front contact I36 of relay iV back contact i3! of relay VP winding of relay CS contact i3 l of relay F in its actuated position and front contact i33 of relay L0 to Relay CS is actuated over this circuit which opens, at its contact N2, the shunt around resistance R for unbalancing the line circuit.

The unbalanced line circuit is effective to pick up relay M in the control office for closing a circuit which picks up relay LIS extending from contact 81 of relay M in its actuated position, back contacts 82 and 83 of relays 3V and 2V respectively, front contact 84 of relay iV, back contact 268 of relay VP, back contact 38 of relay PON and upper winding of relay LIS to Relay LIS closes its previously described stick circuit. At the beginning of the succeeding off period, just before relay FP drops, the indication is executed by closing a circuit extending from (B+), front contact 98 of relay LIS, front contact of relay FP, front contact 2!]! of relay POF, back contacts 262 and 2933 of relays 3V and 2V respectively, front contact 209 of relay EV, bus 2L, front contact 299 of relay IST and winding of relay HR to (ON). This circuit actuates relay 21R to its right hand position.

An executing circuit is closed for actuating relay iIR to its left hand position extending from (13-) back contact 92 of relay EIS, front contact 93 of relay FP, front contact 94 of relay POF, back contacts 95 and 96 of relays 3V and 2V respectively, front contact 91 of relay iV, bus 2E, front contact 2MB of relay IST and winding of relay HR to (CN). With relay 21R. actuated to the right and relay iIR actuated to the left a circuit is closed for lighting normal indicating lamp N which extends from contact 2H of relay 21R in its right hand dotted position, contact 2E2 of relay HR in its left hand position and lamp N to It will be noted that this is a late indication, that is, the line circuit is unbalanced during the latter part of the second on period for indicating that the switch machine is in its normal locked position.

In the event that the switch machine is in its reverse locked position, then the early indication is effected during the second on period by closing a circuit extending from front contact Mi! of relay WP contact me of relay WP in its left hand dotted position, bus 2E back contact M2 of relay 2V front contact I39 of relay IV front contact I31 of relay V'P winding of relay CS contact i34 of relay F and front contact 533 of relay L0 to This circuit is effective to operate relay CS for unbalancing the line circuit during the early part of the on period, that is, before the VP relays are dropped.

This unbalanced condition operates relay M for picking up relay EIS over a circuit extending from contact iii of relay M, back contacts 82 and 83 of relays 3V and 2V respectively, front contact 84 of relay iV, front contact 2% of relay VP and upper winding of relay EIS to Relay EIS sticks as previously described, and the ex cuting circuit is extended through its front contact as from (13+) to bus 2E for actuating relay ill-t to the right. Since relay LIS is not picked up the executing circuit for relay 21B is extended from (B-) at back contact Q8 of relay LIS to bus 2L which actuates relay 21R to the left. in this case reverse lamp R is lighted over a circuit extending from contact 2H of relay 21R in its left hand position and contact 2 i 3 of relay HR in its right hand dotted position.

In the event that the switch is in its unlocked position relay WP will be de-energized so that the circuit leading from contact Mil is ineffective to energize relay CS which results in the line circuit remaining balanced throughout the second on period. This prevents the operation of relay M so that relays EIS and LIS are not picked up which results in (15-) potential being applied to both relays HR and 21R for positioning these relays to the left. With these two relays both positioned to the left both lamps N and R are deenergized as an indication that the switch is in its unlocked condition.

The above example indicates the transmission of three indications during a single step. It is obvious that one more indication can be transmitted during the same step, that is, by energizing both buses 2E and 2L for picking up both relays EIS and LIS in the control office. This condition is not required when used in connection with the transmission of indications relating to the switch machine position, but it is obvious that there are four combinations available at each step which may be used for any purpose desired. For example, a particular step of the cycle could be used for transmitting two pair of indications,

such as occupied or unoccupied condition of the track circuit and the clear or stop indications of the signals associated with this track switch. It is believed that the above example indicates how these various combinations may be made up and it also indicates that additional indications can be transmitted on additional steps of the cycle by energizing the early and late buses such as 3131 3L 4E and @L of Fig. 3B in various combinations.

End of indication cooler-The step-by-stepoperation of the system and the impulsing of the line circuit during an indication cycle are similar to those operations during a control cycle and the line circuit is de-energized following the transmission of the last impulse in a similar manner as previously explained which allows the relays of the system to assume normal positions.

Relay L0 at the field station is dropped when relay SA drops its front contact E38, which de energizes the lower winding of relay L0 before relay SAP closes its back contact 53!. Relay CH is picked up at some step of the cycle so that it will be effective to register a succeeding change in an indication device at this station. The circuit for picking up relay CH is not shown since this feature may be as illustrated in Patent 1,852,402, for example, the details of which are immaterial to an understanding of the present invention.

Lock-out between stations.-As previously mentioned it may happen that changes occur at several stations at the same time or in rapid succession so that more than one field station will have new indications to transmit at the beginning of a cycle. In order to prevent more than one station actually transmitting indications during the same cycle, lock-out means are provided at each station effective to select that field station nearest the control office having new indications to transmit.

When a change occurs at a field station, as for example the first station illustrated in Figs. 3A and 3B resulting in the de-energization of change relay CH the closure of back contact 121 causes lock-out relay L0 to be energized and the system is initiated by the energization of the line circuit picking up relay F in the control office as previously described. The picking up of relay F in the control office effects the picking up of relays STR, SA, AX and SAP during the conditioning period. When relay SA in the control office is picked up an impulse of alternating current is applied to the line for picking up the STR relays at all stations so that these stations will all be initiated into the cycle of operations. The picking up of the STR relays results in the SA and SAP relays at all stations being picked up, all of which has been previously explained.

With the SA relay at a station picked up, the pick-up circuit for the associated lock-out relay is opened at a back contact such as 128 of relay SA In other words, the last chance that a change at a field station has for actively associating this field station with the line circuit ends when the SA relay at that station is picked up. This means that the CH relay at a station must be down for a sufficient period of time prior to the picking up of the associated SA relay to allow the upper winding of the lock-out relay to be energized over the line circuit.

Assuming that the dropping of relay CH picks up lock-out relay L0 to initiate the cycle and that another change relay (relay CH for example which is not shown) drops before the associated SA relay is picked up, then the current applied to the line circuit is effective to pick up the lockout relay (for example relay LO which is not shown) at the second station. The system proceeds through the conditioning period as previously described and at the time the SA relays at the stations pick up their contacts, any lock-out relay (having its contacts picked up) at a station farther out the line from station No. 1 will be deenergized because the opening of the back contact similar to I30 of the SA relays deenergizes the stick circuit for such lock-out relay that may be picked up.

The lock-out relay at any station farther out the line cannot be energized over the line circuit after relay SA at the first station is picked up because of open back contacts I43, I44 and open front contact I03. The lock-out relay at station No. 1 is not released after relay SA picks up its contact I30 because the direct current applied to the line in the control office is extended through the relay LO by way of its front contact 12%, back contact I2! of relay CH upper winding of relay L0 impedance 1M and back contact H33 of relay SAP to the other side of the line. When relay SAP is picked up the stick circuit for relay L0 is completed through front contacts 130, l3l and I32 before the energizing circuit for relay L0 including the line circuit, isopened at back contact !03 of relay SAP Since the picking up of the SA relay at any station farther out the line drops the associated lockout relay if it has been picked up and since the line circuit is not energized after the picking up of the SA relay until the SAP relays are picked up, there is an interval of time during which the lock-out relays at these farther stations cannot be energized through either winding. From the above it will be noted that the dead line for picking up the lock-out relays is at the time the associated SA relays pick up. Also the look-out period during which any lock-out relay which is picked up at an inferior station is dropped extends from this dead line up to the time of picking up the SAP relays. Since no lock-out relay can be picked up after the dead line is passed and since any lock-out relay at any inferior station which might have been picked up during the same conditioning period that a lock-out relay at a superior station was picked up, the look-out period functions to drop out any of these inferior lock-out relays.

Although the lock-out functions have been explained with reference to the first and other field stations of the system it will be understood that similar conditions may exist between various com-- binations of stations, but it is believed that the explanation given is sufficient for an understanding of all such combinations when the fact is kept in mind that the nearest station to the control of 2 fice with its lock-out relay picked up before the dead line is reached is a superior station and all others which may be picked up at this time are inferior stations and will be dropped out when the system passes this dead line.

Front contact M4 on relay CH which bridges back contact I43 of relay SA is for the purpose of preventing a station near the control ofiice having no indications to transmit, interrupting the continuity of the line circuit by opening back contact I43 of its SA relay at the start of the cycle. By bridging contact N33 with front contact M4 the line circuit is maintained complete at those stations not having indications to transmit because at such stations the CH relays remain picked up. It will of course be understood that at those stations having new indications to transmit the dropping of the CH relays is effective to operate the look-out circuits as above described. The CH relays at transmitting stations are picked up after the associated station has completed its transmission in a manner disclosed for example in Patent 1,852,402.

Duplex operation.-It has been pointed out that control and indication cycles may each occur separately or simultaneously. The operation for control and indication cycles alone has been described and it will now be pointed out how the sys tem operates when controls and indications are transmitted during the same cycle.

The actuation of a starting button in the control oflice picks up its associated storing relay. During the time that the system is at rest and any time up to the end of the period marked off by the picking up of back contact 9 of relay SA, the CD relay associated with the actuated starting button can be picked up to mark the cycle as one for the transmission of controls. In other Words, if a field station has initiated the system and the SA relay has been picked up the control ofilce cannot make use of the system for the transmission of controls during this cycle because of open back contact 9 but must wait until the beginning of the next cycle.

On the other hand a lock-out relay such as relay LO at a field station may be picked up at any time during the energized condition of the line circuit from the control ofiice battery B at the start of a cycle. In other words, a lock-out relay at a field station may be picked up at the beginning of a cycle any time up to the picking up of back contacts I2 and M of relay SA in the control office. After these contacts are picked up no field station can actively associate itself with the line circuit for the transmission or" its indications until the beginning of another cycle, because when relay SAP in the control office is picked up to again connect direct current to the line circuit the SAP relays at the field stations will be picked up so that the upper windings of the look-out relays will be open at back contacts similar to I03.

Thus under the condition that the system is initiated by the picking up of a CD relay in the control ofilce and a lock-out relay at a field station both controls and indications are transmitted during the succeeding cycle. The polarity of each impulse applied to the line circuit is determined by the code jumper and lever connections selected by the CD relay which is picked up. The selection of a particular field station for the transmission of indications is determined by the particular lock-out relay which is picked up when impulsing begins and this particular lock-out relay determines the combination of balanced and unbalanced conditions of the bridge circuit for the succeeding steps of the cycle. Since controls are transmitted outward from the control mice and since indications are transmitted inward to the control office by the independent conditioning of the two-wire line circuit these controls and indications may be transmitted simultaneously during the same cycle or" operation.

Since the transmission of out-bound and inbound messages have been explained in detail for separate cycles of operation and since the line circuit is distinctively conditioned in a separate and distinctive manner for the transmission of out-bound and in-bound messages when both the control oflice and a field station have messages ready to transmit at the same time at the beginning of a cycle as above described, it is not believed necessary to describe these operations in detail during a duplex cycle. The individual circuit operations are the same as already described for separate cycles. It has also been mentioned that when controls alone are transmitted the inherent code combination applied to the bridge circuit which results from a control cycle is not effective to register a field station in the control oifice. This combination is a combination of the line circuit remaining balanced throughout the steps of the cycle for forming a phantom code. Similarly when indications alone are transmitted the line circuit is impulsed with a series of impulses which forms a phantom code and which does not select any station for controls.

Although one specific embodiment of the invention has been shown it is to be understood that various rearrangements may be made and still come within the scope of the invention.

Having thus described a centralized trafilc con- 'trolling system as one specific embodiment of the present invention it is desired to be understood that this form is selected to facilitate in the disclosure rather than to limit the number of forms which the invention may assume and it is further to be understood that various modifications, adaptations and alterations may be applied to the specific form shown to meet the requirements of practice without in any manner departing from the spirit or scope of the present invention except as limited by the appended claims.

What I claim is:

1. In a centralized traffic controlling system, a control oifice and a. plurality of field stations connected by a line circuit, step-by-step mechanism at said ofiice and at said stations operated in synchronism through a cycle by a plurality of impulses applied to said line circuit, a message receiving relay connected to said line circuit in said ofiice, means at each of said stations for selectively connecting a resistance in said line circuit at each step of said cycle, means responsive to said selective connection for selectively energizing said relay when a station is transmitting, means in said ofiice controlled at each step of said mechanism for preventing the flow of current through the winding of said relay when said line circuit is deenergized and when said line circuit is energized with said resistance excluded, and means responsive to the energized and deenergized conditions of said relay at each step of said cycle for registering the identity of the calling station in said office.

2. In a centralized traific controlling system, a control oifice and a plurality of field stations connected by a line circuit, step-by-step mechanisms at said oilice and at said stations operated in synchronism through a cycle by a plurality of impulses applied to said line circuit, a message receiving relay connected to said line circuit in said ofiice, means at each of said stations for selectively connecting a resistance in said line circuit at each step of said cycle, means responsive to said selective connection for selectively energizing said relay when a station is transmitting, means in said ofiice controlled at each step of said mechanisms, for preventing the flow of current through the winding of said relay when said line circuit is deenergized and when said line circuit is energized with said resistance excluded, and means responsive to the energized and deenergized conditions of said relay at each step 01' said cycle for registering the identity of the calling station in said office and for registering messages in said office from a calling station.

3. In a centralized traffic controlling system, a control oflice and a plurality of field stations connected by a line circuit, step-by-step mechanisms at said ofiice and at said stations operated in synchronism through a cycle by a plurality of impulses applied to said line circuit, a message receiving relay connected to said line circuit in said ofiice, means at each of said stations for selectively connecting a resistance in said line circuit at each step of said cycle, means responsive to said selective connection for selectively energizing said relay when a station is transmitting, means in said office controlled at each step of said mechanisms for preventing the fiow of current through the winding of said relay when said line circuit is deenergized and when said line circuit is energized with said resistance excluded, means responsive to the energized and deenergized conditions of said relay at each step of said cycle for registering the identity of the calling station in said office and for registering messages in said office from a calling station, and means for pre- 

